Yesterday Mozilla introduced a new Firefox project, called JetPack, that could revolutionize the extensibility of Firefox. Currently available as a Firefox extension, JetPack allows users to extend their browser using regular HTML, JavaScript, and CSS. So far JetPack seems to us sort of like a hybrid between a normal extension and Greasemonkey user scripts; using new JetPack functionality requires a page refresh and not a browser restart (like Greasemonkey), but JetPack can add elements to the user chrome (like extensions). It's a tool that'll probably interest developers most for the time being, but JetPack's functionality could be the futureof Firefox extensions down the road. [JetPack via Mozilla Labs]